Google+ is a little over three weeks old now, and despite the social network's current invite-only testing phase, it has grown by leaps and bounds in its short time on the internet. In fact, Google+ just hit 20 million users.

ComScore, a Web-traffic watcher, has estimated that Google+ has had 20 million different visitors since the launch of the site. About five million of these users are from the United States.

ComScore uses a global measurement panel of two million internet users to develop its estimates.

"I've never seen anything grow this quickly," said Andrew Lipsman, vice president of industry analysis at comScore.

Google+, which launched June 28, 2011, is a social networking service that offers a range of features including "Circles," which allows users to organize contacts; "Hangouts," which is a video chat feature; "Huddle," a mobile feature for group instant messaging; "Sparks," a search engine for sharing mutual interests, and of course, the +1 feature, which Google+ users can use to say they agree with or like a topic.

Many wondered if Google+ would be a suitable rival for other social networks like Facebook and Twitter. For instance, Facebook CEO Mark Zuckerberg has said that Facebook is already established with 750 million users and that his site will not lose appeal to Google+'s features. In addition, LinkedIn CEO Jeff Weiner questioned the purpose of Google+ when all the social network bases are already covered: Facebook for family and friends, LinkedIn for professionals, and Twitter for "microcasting" your thoughts.

But both rival CEO's may be eating their words as Google+ gains more and more users. With Google+ becoming so popular so quickly, Google could benefit in other areas through the use of social integration.

"Given positive initial traction from users, we believe Google is now better positioned to compete and integrate social cues across its products than before, which could drive increased relevancy in search going forward," said Barclays Capital equity researchers.

"Google fired a shot heard 'round the world, and now a second American company has answered the call to defend the rights of the Chinese people." -- Rep. Christopher H. Smith (R-N.J.)